List of products in the National Drug Code with proprietary name . This medication is used to treat high blood pressure. Lowering high blood pressure helps prevent strokes, heart attacks, and kidney problems. Methyclothiazide is a "water pill" (diuretic) that causes your body to get rid of extra salt and water. This increases the amount of urine you make. This medication also reduces extra fluid in the body (edema) caused by conditions such as congestive heart failure, liver disease, and kidney disease. Getting rid of extra water helps to reduce fluid in the lungs so that you can breathe easier. It also helps to decrease swelling of the arms, legs, and stomach/abdomen.